I purchased these for my 7th grade history classes while we were studying the Byzantine Empire, during which time mosaics were very popular. Mosaic project fit in well with our curriculum, and the students had fun making the coasters. I ordered extra sets just to have extra tiles on hand, because certain colors go quickly. We left the frames unfinished, and I later sprayed them with an acrylic fixative. I wouldn't use them as coasters, but as decorative objects. 7th graders easily completed the project in a class period.